(1) Field of the Invention
The present invention relates to a radar system with a self-diagnosis function.
(2) Description of the Related Art
In recent years, various technologies regarding radar systems equipped in vehicles (hereinafter, referred to as “in-vehicle radar systems”) have been developed. The in-vehicle radar systems, which play roles in security, should be checked at starting or during operation to diagnose that the systems operate normally without any errors. Such diagnosis can be realized for the following three-type radar systems.
The radar system of the first type is shown in FIG. 1. This radar system 10 performs self-diagnosis on a receiving unit 21 and a transmission unit 22, using leakage signals between a transmission antenna 16 and a receiving antenna 11. In the radar system 10, a displacement oscillation circuit 14 emits signals having frequency for self-diagnosis, and the transmission antenna 16 outputs the signals. During self-diagnosis the receiving antenna 11 is also activated, and an analysis processing circuit 13 analyzes dimension (frequency, for example) of the signals received by the receiving antenna 11. Here, a collation circuit 23 collates transmitted frequency and received frequency, and abnormality of the system is determined based on the result of the collation (refer to Japanese Unexamined Patent Application Publication No. 2001-116828, for example).
The radar system of the second type determines abnormality of the system in the following manner. In the radar system, a part of radio waves which the radar system transmits is received by a detection antenna, and then provided to a delay transmission line. Then, beat signals generated in the delay transmission line are filtered by a band-pass filter and eventually analyzed to determine the abnormality. In this radar system, a delay amount (length) of the delay transmission line is set to be equivalent to the distance out of a range of detection (refer to Japanese Unexamined Patent Application Publication No. 2003-207561, for example).
The radar system of the third type detects a failure of the system, by determining abnormality of a multiplexer which multiplexes outputs of an oscillator. This radar system is equipped with a function of monitoring drain voltage generated in the multiplexer, and uses outputs of the function to determine abnormality (refers to Japanese Unexamined Patent Application Publication No. H05-341032, for example).
However, each of these radar systems of the prior arts needs the displacement oscillation circuit which emits signal patterns for the diagnosis and the analysis processing circuit in order to diagnose abnormality of the radar system, so that the radar system would be expensive and complicated.
In order to address the above problem, an object of the present invention is to provide a radar system which can easily diagnose abnormality of the system, using a simple and inexpensive structure.